Cannot figure out where to load javascript file

Question

HTML

<!DOCTYPE html>
<html lang="en">

<head>

    <meta charset="utf-8">
    <title>Game</title>
    <link rel="stylesheet" type="text/css" href="stylesheet.css">
    <script src="script.js"></script>   

</head>

<body>

    <div class="container">

    <table class="table ">
        <tr>
            <td id="1">a</td>           
            <td id="2">a</td>           
            <td id="3">a</td>           
            <td id="4">a</td>
        </tr>
        <tr>
            <td id="5">a</td>           
            <td id="6">a</td>           
            <td id="7">a</td>           
            <td id="8">a</td>
        </tr>
        <tr>
            <td id="9">a</td>           
            <td id="10">a</td>          
            <td id="11">a</td>          
            <td id="12">a</td>
        </tr>
        <tr>
            <td id="13">a</td>          
            <td id="14">a</td>          
            <td id="15">a</td>          
            <td id="16">a</td>
        </tr>
    </table>

    </div>


</body>

function startFunction() {
    var table = document.querySelector('#table');
    var table_cells = table.querySelectorAll('td');   
}


window.onload = function() {
  startFunction();
};

I keep getting an error of "uncaught typeError: cannot read property 'querySelectorAll' of null."

I think this has to do with the fact when I'm calling a function that tries to grab said element node before it exists perhaps?

I'm loading my Javascript file in the <head> section of my HTML file so I added a window.onload function to make sure everything is loaded before the page runs. However, I still keep getting this error.

Could you add the accompanying HTML markup to your question please? — Cᴏʀʏ, Jan 19 '17 at 18:52
Your code should work fine. Are you sure your table has `id="table"`? — Tyler Roper, Jan 19 '17 at 18:53
Santi's answer is correct. An additional improvement would be to use `document.addEventListener('DOMContentLoaded', function() { ... });` instead of `window.onload = ...`. Here's a good question and answer on the topic: http://stackoverflow.com/questions/799981/document-ready-equivalent-without-jquery — Jordan Running, Jan 19 '17 at 19:00
From the linked question: "`window.onload` fires after all images, frames, etc. have been loaded." Usually you only want to wait until the DOM has finished loading, ergo DOMContentLoaded. — Jordan Running, Jan 19 '17 at 19:09
And, as the first paragraph of the [DOMContentLoaded docs](https://developer.mozilla.org/en-US/docs/Web/Events/DOMContentLoaded) on MDN reads: "The DOMContentLoaded event is fired when the initial HTML document has been completely loaded and parsed, without waiting for stylesheets, images, and subframes to finish loading. A very different event `load` should be used only to detect a fully-loaded page. It is an incredibly popular mistake to use `load` where DOMContentLoaded would be much more appropriate, so be cautious." — Jordan Running, Jan 19 '17 at 19:11

Tyler Roper · Answer 1 · 2017-01-19T18:56:52.897

3

Take a look at this line in your JavaScript:

var table = document.querySelector('#table');

The pound-sign indicates an ID, and so your javascript is looking for an element with the ID of "table".

But, if you look at your table, it doesn't have an ID; only class.

The solution is to give your <table> an ID of "table" so that the javascript properly finds it:

<table id="table">

edited Jan 19 '17 at 18:56

answered Jan 19 '17 at 18:54

Tyler Roper

20,529
6
30
51

That was it! Thank you so much. I kept thinking it was something about where I was loading the javascript file. – Faique Moqeet Jan 19 '17 at 18:56
I ended up just using (".table) and ...That should just as fine, right?
– Faique Moqeet Jan 19 '17 at 18:58
That will work, yes, just be aware that classes can apply to multiple elements. – Tyler Roper Jan 19 '17 at 18:59

score 1 · Answer 2 · answered Jan 19 '17 at 18:55

1

The table is missing id attribute. Instead, it has class attribute. Fix by adding id

<table class="table" id="table">

Or modify your query selector to select by class:

var table = document.querySelector('.table');

answered Jan 19 '17 at 18:55

Adam Azad

10,675
5
25
63

Cannot figure out where to load javascript file

2 Answers2